Cleanup and Decommissioning of A Nuclear Reactor After A Severe Accident | IAEA

(1)

TECHNICAL REPORTS SERIES No. 346

(2)

(3)

CLEANUP AND DECOMMISSIONING

OF A NUCLEAR REACTOR

AFTER A SEVERE ACCIDENT

(4)

T h e f o l l o w i n g States a r e M e m b e r s of t h e International A t o m i c E n e r g y A g e n c y :

AFGHANISTAN HOLY SEE PANAMA

ALBANIA HUNGARY PARAGUAY

ALGERIA ICELAND PERU

ARGENTINA INDIA PHILIPPINES

AUSTRALIA INDONESIA POLAND

AUSTRIA IRAN, ISLAMIC REPUBLIC OF PORTUGAL

BANGLADESH IRAQ QATAR

BELARUS IRELAND ROMANIA

BELGIUM ISRAEL RUSSIAN FEDERATION

BOLIVIA ITALY SAUDI ARABIA

BRAZIL JAMAICA SENEGAL

BULGARIA JAPAN SIERRA LEONE

CAMBODIA JORDAN SINGAPORE

CAMEROON KENYA SLOVENIA

CANADA KOREA, REPUBLIC OF SOUTH AFRICA

CHILE KUWAIT SPAIN

CHINA LEBANON SRI LANKA

COLOMBIA LIBERIA SUDAN

COSTA RICA LIBYAN ARAB JAMAHIRIYA SWEDEN

COTE D'lVOIRE LIECHTENSTEIN SWITZERLAND

CUBA LUXEMBOURG SYRIAN ARAB REPUBLIC

CYPRUS MADAGASCAR THAILAND

CZECHOSLOVAKIA MALAYSIA TUNISIA

DEMOCRATIC PEOPLE S MALI TURKEY

REPUBLIC OF KOREA MAURITIUS UGANDA

DENMARK MEXICO UKRAINE

DOMINICAN REPUBLIC MONACO UNITED ARAB EMIRATES

ECUADOR MONGOLIA UNITED KINGDOM OF GREAT

EGYPT MOROCCO BRITAIN AND NORTHERN

EL SALVADOR MYANMAR IRELAND

ESTONIA NAMIBIA UNITED REPUBLIC OF

ETHIOPIA NETHERLANDS TANZANIA

FINLAND NEW ZEALAND UNITED STATES OF AMERICA

FRANCE NICARAGUA URUGUAY

GABON NIGER VENEZUELA

GERMANY NIGERIA VIET NAM

GHANA NORWAY YUGOSLAVIA

GREECE PAKISTAN ZAIRE

GUATEMALA ZAMBIA

HAITI ZIMBABWE

T h e A g e n c y ' s Statute w a s a p p r o v e d o n 2 3 O c t o b e r 1 9 5 6 by t h e C o n f e r e n c e o n the Statute of t h e I A E A held at U n i t e d N a t i o n s H e a d q u a r t e r s , N e w Y o r k ; it e n t e r e d into f o r c e o n 2 9 J u l y 1957. T h e H e a d - q u a r t e r s o f t h e A g e n c y a r e situated in V i e n n a . Its p r i n c i p a l o b j e c t i v e is " t o a c c e l e r a t e a n d e n l a r g e t h e c o n t r i b u t i o n of a t o m i c e n e r g y to p e a c e , health a n d p r o s p e r i t y t h r o u g h o u t the w o r l d " .

P e r m i s s i o n to r e p r o d u c e o r translate t h e i n f o r m a t i o n c o n t a i n e d in this p u b l i c a t i o n m a y b e o b t a i n e d by w r i t i n g to t h e I n t e r n a t i o n a l A t o m i c E n e r g y A g e n c y , W a g r a m e r s t r a s s e 5 , P . O . B o x 100, A - 1 4 0 0 V i e n n a , A u s t r i a .

P r i n t e d b y t h e I A E A in A u s t r i a D e c e m b e r 1992

(5)

TECHNICAL REPORTS SERIES No. 346

CLEANUP AND DECOMMISSIONING OF A NUCLEAR REACTOR

AFTER A SEVERE ACCIDENT

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1992

(6)

VIC Library Cataloguing in Publication Data

Cleanup and decommissioning of a nuclear reactor after a severe accident.

— Vienna : International Atomic Energy Agency, 1992.

p. ; 24 cm. — (Technical reports series, ISSN 0074-1914 ; 346) STI/DOC/10/346

ISBN 92-0-104492-5

Includes bibliographical references.

1. Nuclear reactors—Decommissioning. 2. Radioactive decontamination. 3. Nuclear reactors—Accidents. I. International Atomic Energy Agency. II. Series: Technical reports series (International Atomic Energy Agency) ; 346.

VICL 92-00041

(7)

FOREWORD

Although the development of commercial nuclear power plants has in general been associated with an excellent record of nuclear safety, the possibility of a severe accident resulting in major fuel and core damage cannot be excluded and such accidents have in fact already occurred. For over a decade, IAEA publications have provided technical guidance and recommendations for post-accident planning to be considered by appropriate authorities. Guidance and recommendations have recently been published on the management of damaged nuclear fuel, sealing of the reactor building and related safety and performance assessment aspects. The present technical report on the cleanup and decommissioning of reactors which have undergone a severe accident represents a further publication in the series.

A Technical Committee meeting on the present subject was held in Vienna from 24 to 28 June 1991 (IAEA Scientific Secretary, P.L. De of the Division of Nuclear Fuel Cycle and Waste Management). The meeting was attended by ten experts from nine Member States. The participants discussed and revised a preliminary report written by V.A. Kremnev (former USSR), R. Graf (Germany), J.H.

Leng (United Kingdom), R.I. Smith (USA), A.A. Borovoi (former USSR), T.V.

Efimova (former USSR) and the IAEA Scientific Secretary Z. Dlouhy of the Divi- sion of Nuclear Fuel Cycle and Waste Management. After the meeting, the report was revised by the IAEA Scientific Secretary, M. Laraia, of the Division of Nuclear Fuel Cycle and Waste Management, with the assistance of two outside consultants, J.H. Leng (United Kingdom) and C. Bergman (Sweden), and the final report was approved by the members of the Technical Committee. Acknowledgement is due to J.F. Zuber (Switzerland) for providing detailed information on the decommissioning of the Lucens reactor.

(8)

(9)

1. INTRODUCTION

1.1. BACKGROUND

During the siting, design, construction and operation of nuclear facilities, the protection of operating personnel, the general public and the environment is a primary concern. Therefore, from the very beginning of the peaceful utilization of nuclear energy, nuclear power plants have been designed to deal with unanticipated occurrences and accidents. In order to minimize potential radioactive releases from the reactor core to the environment, containment systems have been used in most cases. During the last decade, some nuclear power plants have also been provided with emergency containment venting systems. Although the probability of severe accidents is low, their occurrence cannot be entirely excluded, as experience shows.

The Three Mile Island (TMI-2) accident in 1979 and the Chernobyl accident in 1986 accelerated studies in accident recovery. In addition to national efforts, many international organizations, such as the IAEA, the Nuclear Energy Agency of the OECD (OECD/NEA), the former Council for Mutual Economic Assistance (CMEA) and the Commission of the European Communities (CEC), have inves- tigated or are investigating this area.

Since the early 1980s, IAEA documents have provided technical guidance and recommendations for emergency planning to be considered by appropriate authorities [1-4]. In particular, the IAEA has been active in planning for emergency pre- paredness against the possibility of situations where a severe accident may involve the need of on-site and off-site remedial actions and protective measures [5-8].

Guidance and recommendations have recently been published for the management of damaged nuclear fuel [9], sealing of the reactor building [10] and related safety and performance assessment aspects [11]. A catalogue of tools, methods and analyti- cal techniques that would be of particular value during accidents, even those of much lesser magnitude than TMI-2 and Chernobyl, was recently published by the IAEA [12]. Operating experience and guidance on managing abnormal wastes, in particular those arising from accidents, can be found in Ref. [13]. The present technical report is a further step in the series of IAEA publications dedicated to this task. For the purpose of this report, a severe accident is one in which the reactor suffers major fuel and core damage. Such damage could occur without failure of the containment, as in the TMI-2 accident, and therefore with few off-site consequences, or with major containment failure as in the Chernobyl accident, where serious off-site problems arose.

Immediately after a severe accident has occurred, all efforts are directed towards bringing the accident under control and implementing those measures needed to protect the public and the workers, i.e. prevent recriticality, cool the reactor core, put out fires, and reduce or stop any major spread of radionuclides. These

(12)

(13)

emergency actions are all part of the management of the accidental situations and are covered in other IAEA reports [6, 9, 13]. Once the accident control is complete and the reactor facility is in a stable state, consideration of the possible options for managing the damaged facility and any off-site consequences should be initiated.

After cleanup of the facility, the two main alternatives are:

(a) Rehabilitation and reuse of all or part of the facility;

(b) Decommissioning using immediate dismantling or dismantling after a period of safe storage.

The choice will depend largely on technical and economic factors such as the amount of damage to the core and containment, the spread of radioactive material, the availability of resources to complete the option and the need for the site. However, political factors and public attitudes can also have a significant impact and may result in decommissioning being chosen although rehabilitation might be the preferred choice from the technical and economic viewpoints.

1.2. OBJECTIVE

The objective of this report is to provide an overview of factors relevant to the identification of cleanup requirements and to the choice of a decommissioning option for a severely damaged nuclear power plant. A methodology is proposed to evaluate various options and to select an appropriate action in a particular accident situation.

The report should serve national authorities concerned with handling severe accidents, and the various organizations and operating personnel involved in collect- ing and evaluating the necessary information for the decision making process. It should also assist the regulatory authorities in identifying parameters relevant to the safety and environmental assessment of the selected option.

1.3. SCOPE

The report briefly describes the overall post-accident management sequences, including off-site cleanup, on-site cleanup and stabilization, and the possibility of rehabilitation and decommissioning. In Fig. 1, the interrelationships between the various activities are shown diagrammatically and the scope of the report in the context of these activities is indicated. However, the main part of the report presents a basic framework for identifying the cleanup requirements and determining the optimum decommissioning option for a severely damaged reactor.

Even if the reactor is to be decommissioned, there may be cases where parts of the facility can be reused after proper cleanup and rehabilitation. Once a decision is taken to rehabilitate a facility or part of a facility, all further actions related to the rehabilitation are outside the scope of this report.

(14)

It is recognized that, ideally, the taking of preventive actions during the construction of a nuclear facility might reduce the doses and costs for decommissioning should an accident occur. Generally, such actions are not considered justified for that sole purpose. However, they can be justified and implemented for other reasons, e.g.

to facilitate operation, maintenance and normal decommissioning [14] and as a component of a programme to mitigate the consequences of severe accidents; as such they are, however, outside the scope of this report.

Although the information presented here is intended to cover severe accidents in nuclear power plants, it can also be used for other reactor types, such as research or prototype reactors. Although not specifically discussed, other facilities (reprocessing plants, fuel processing and fabrication facilities, etc.) are to a certain degree encompassed by the methodology of this report.

2. MANAGEMENT AFTER A SEVERE REACTOR ACCIDENT

2.1. MANAGEMENT STRATEGY

Immediately after the accident, the first activity is the actual management of the accident to a point where the immediate safety problems have been controlled.

The main thrust is towards the cleanup and selection of the decommissioning option which is to be implemented. The content of each activity represented in Fig. 1 will be expanded in Sections 2.2-2.7.

2.2. MANAGEMENT OF EMERGENCY PHASE

Although outside the scope of this report, accident management includes the efforts aimed at bringing the situation under control. This comprises the steps necessary to ensure that:

(i) Recriticality cannot occur except as a result of significant changes to the system.

(ii) All fires and other severely exothermic chemical reactions have been termi- nated and controlled.

(iii) There is no continuing major release of radionuclides.

(iv) Heat removal is adequate to maintain safe temperatures for the remaining materials.

This phase also includes the implementation of protective measures deemed necessary by the emergency director [5].

(15)

2.3. OFF-SITE C L E A N U P .

Off-site cleanup is not within the scope of the report as it is covered in Refs [5-8], To ensure that unnecessary off-site contamination is not created as a result of the on-site cleanup and stabilization, and, later on, of decommissioning activities, it is necessary to consider the off-site impacts during planning of the on- site work (Section 3.3).

2.4. ON-SITE CLEANUP AND STABILIZATION

Considerable guidance is given in Ref. [9] on the cleanup phase, but with specific emphasis on the handling of the fuel and associated waste. The present report is more general in that it considers cleanup of the plant and buildings and, in particular, recognizes that in severe accident situations it may be necessary to have a phased cleanup strategy interacting with analysis and assessment, each cleanup phase allow- ing access to further areas for detailed measurement and examination. Primarily, the post-accident on-site cleanup process is aimed at removing or fixing contamination, reducing radiation levels in working areas, removing fuel and gathering data on the extent of the damage caused by the accident. Because, in general, radiation levels will be higher than in a normally shut down plant, exposure control and dose reduction techniques will gain in importance and some or all of the methods given in Ref. [15] will need to be considered. The accounts of severe accidents given in the Annex demonstrate that the assessment and cleanup phases can last a considerable time. During the cleanup phase it is likely that waste types and volumes will differ from normal operational wastes and special provisions for treatment and disposal will be required, as discussed in Ref. [13].

As a consequence of the cleanup and assessment process, the information which will be necessary to decide whether rehabilitation is economically and technically possible will be accumulated.

2.5. THE DECISION — DECOMMISSION OR REHABILITATE

After the damaged reactor has been stabilized and cleanup has been initiated, the decision whether to decommission or rehabilitate can be considered. In the extreme case where damage is so severe that meaningful rehabilitation is impossible, this decision is simple; where damage is not so severe the decision to rehabilitate will be complex and should be based on a number of factors:

(i) Whether the costs of further decontamination, refurbishment of the plant and the potential additional measures which may be required will lead to a saving compared with the construction of a new plant, including an allowance for the decommissioning of both the old and new plants.

(16)

(ii) Whether the collective dose associated with the rehabilitation work, the operation of the rehabilitated plant and its final decommissioning will be unacceptable compared to the collective dose associated with the decommissioning of the damaged plant and the operation and decommissioning of a new plant.

For the economic side of the equation there will be a number of additional considerations which may be difficult to quantify and which can only be handled by some form of economic risk analysis. Examples are:

(a) The perceived value of not having to go through the full planning and approval process for a new plant on a new site, including the risk the application may fail or the process be excessively delayed.

(b) The risk that the refurbished plant may have difficulties in obtaining regulatory approval to recommence operation or could obtain such approval only after costly and time consuming modifications.

Finally, special local conditions such as public opinion and political considerations may weight the balance one way or another, making the detailed economics less important.

2.6. REHABILITATION

In the context of this report, rehabilitation refers to the cleanup and rebuilding of the reactor for reuse. However, on a nuclear site there are many installations which normally are not contaminated to any significant extent. If these are not affected by the accident, they can easily be put back into operation or be used for other non-radiological purposes. If simple decontamination to exemption levels is carried out, this can be considered as decommissioning to Stage 3 (see Section 2.7) and thus to be covered by this report.

2.7. ASSESSMENT OF DECOMMISSIONING OPTIONS

Because of the additional problems created by the accident, decommissioning of reactors which have suffered a severe accident will normally be subject to more technical uncertainty than is the case with a plant which has been shut down at the end of its economic or design life. As a result, it will be less straightforward to assemble the information necessary to make an optimum decision between decommissioning options. The main purpose of this report is to set out the steps required and the important parameters to be considered in arriving at a final decision.

(17)

In order to provide a well understood framework for the discussions, the IAEA definitions of a three stage decommissioning process are utilized. Under normal circumstances, fuel removal from the reactor is considered a prerequisite for decommissioning activities to proceed. The detailed definitions of the three stages are given in Ref. [16] and are summarized below:

Stage 1 (storage with surveillance). During this stage, the first contamination barrier is kept as it was during operation. But mechanical openings are permanently sealed. The containment building is kept closed and under institutional control. Sur- veillance, monitoring and inspections are carried out to ensure that the plant remains in good condition.

Stage 2 (restricted site release). In this stage, the first contamination barrier is reduced to minimum size by removing easily dismantled parts. Sealing of the barrier is reinforced by physical means and the biological shield is extended, if necessary, to completely surround the barrier. After decontamination, the containment building may be modified or removed if it is no longer required for radiological safety. Access to the building can be permitted. The non-radioactive buildings on the site can be used for other purposes.

Stage 3 (unrestricted site use). All materials, equipment and parts of the plant still containing significant levels of radioactivity are removed. The plant and site are released for unrestricted use. No further inspection or monitoring is required.

After a severe accident, the removal of all fuel may be impossible without at least partial dismantling to gain access and thus it may not be possible to fit the actually achievable states into the formal definitions of Stages 1 and 2; however, the concepts are useful as a baseline against which deviations can be discussed.

The final state of the site which can in practice be achieved, whether completion occurs within a few years or over a hundred years or more after the accident, will be very much dependent on the severity of the original accident. For Chernobyl, for example, it is difficult to imagine that it would be either cost-effective or dose- effective to attempt to return the site to unrestricted use (Stage 3), in the short or even medium term, while for TMI-2 Stage 3 would be an achievable target (see Annex). However, conversion of a damaged reactor to a waste repository is possible if a safety and environmental impact assessment shows compliance with relevant criteria and requirements.

It should be noted that there are national definitions of decommissioning alternatives which differ from those promulgated by the IAEA. Also, many Member States do not consider decommissioning completed until the site is available for unrestricted use.

(18)

3. FACTORS RELEVANT TO CLEANUP AND DECOMMISSIONING AFTER A SEVERE ACCIDENT

3.1. RADIOLOGICAL PROTECTION

The main objectives of all post-accident measures are to ensure that humans and the environment are adequately protected against exposure and contamination from radioactive material originating from the facility and to reduce residual contamination levels to a minimum. This protection should be achieved both during the different types of intervention such as sheltering and during cleanup and stabilization and eventual dismantling of the facility.

The International Commission on Radiological Protection (ICRP) has in its recent recommendations [17] expanded the system of radiological protection based on justification, optimization and dose limitation introduced first in Ref. [18] to more explicitly include cleanup and stabilization after an accident. This system was expanded in the IAEA Basic Safety Standards on Radiation Protection [19].

Facilities which have been exposed to a severe accident are most probably heavily contaminated. In addition, ancillary systems such as ventilation and waste management systems may not be fully operating. Although work in such environ- ments requires extra radiological precautions to be taken, the possibility cannot be excluded that occupational exposure might be higher than during normal maintenance and decommissioning work. In all situations, however, the dose limits established by the national authorities must be met.

The optimization of radiological protection requires the evaluation of collective doses for all available options. Although in most cases this evaluation will be dominated by the occupational doses, the doses and risks to the general public as a result of the spread of radioactive material must not be neglected.

3.2. SAFETY CONSIDERATIONS PERTAINING TO THE FACILITY STATUS Throughout each stage of the progression from the termination of the accident sequence, through plant cleanup and stabilization, to long term storage and eventual dismantling, there are general safety related issues that must be examined. These include:

(a) Determining the potential for recriticality as a result of long term changes in the geometry of the remaining fissile material or other long term physical, chemical or biological concentration mechanisms;

(b) Determining the potential for unacceptable heating to occur as a result of changes to heat removal paths reducing the capacity to remove the decay heat;

(19)

(c) Evaluating the potential for chemical reactions within the debris to cause either heat release or the generation of flammable or explosive gas mixtures or locally higher pressures;

(d) Controlling the spread of contamination, including leaching and other disper- sive mechanisms;

(e) Maintaining the integrity of the containment as a structure and as a barrier to prevent further release (this issue should include an estimate of the probable operational life of such barriers without major remedial work);

(f) Utilizing auxiliary systems in cleanup and decommissioning work; and (g) Evaluating the reliability of existing reactor logging and radiological

monitoring equipment.

As the facility progresses through the stages of decommissioning, these safety related issues should be continually evaluated until the hazard has been eliminated.

The preliminary assessment to determine the hazards related to steps taken to stabilize the facility must of necessity be largely theoretical, based on what is known about the reactor materials and what can be seen by remote viewing techniques without interaction with the structure. One objective of the preliminary assessment is to establish what sampling and other monitoring procedures can be deployed without danger of creating new problems.

After the preliminary assessment of the hazards of intervention has been made, work can start on the main assessment of the status of the facility to permit cleanup to start. The difficulty in characterizing the state of the plant will depend on the spread of contamination through the building and the radiation field directly arising from the damaged reactor. Therefore, even at this early assessment stage, it may be necessary to decontaminate some areas as well as to erect temporary radiation shielding to get the required access. As emphasized earlier, it is essential to perform an adequate assessment of the potential consequences of the changes to the system which might result from efforts to characterize the facility. This in turn could in itself lead to further work requirements such as the introduction of a locally controlled and filtered ventilation system. Ultimately, the assessment work has to provide the data necessary to make the correct choice between the various decommissioning options.

The type of information which needs to be gathered and assessed includes:

(a) Inventory of the radioactive and fissile materials associated with the plant. This will involve calculations from a detailed irradiation history of the fuel charge, a detailed operational history of the reactor itself and as much information as can be collected on the exact composition, including trace elements, of all materials subject to neutron activation.

(b) Radiation contours around the reactor and in adjacent connected buildings, including the distinction between radiation coming directly from the damaged reactor and that coming from dispersed contamination.

(20)

(c) The quantity, isotopic content and time distribution of present and potential airborne contamination.

(d) The quantity and isotopic composition of the solid deposition and the degree of penetration into surfaces.

(e) The chemical and physical form of the radioactive materials, with particular emphasis on unusual phases or compounds which may have been generated either in the initial accident or as a result of efforts to terminate the accident.

(f) The mechanical stability of the remaining structures and, in particular, their residual resistance to seismic activity or any other disturbing agents such as severe gales and floods.

(g) Modifications to ventilation and cooling flow paths occasioned by structural changes as a result of the accident or remedial actions.

(h) Results of a detailed examination of the main reactor components, with estimates of the degree of damage.

(i) The status of auxiliary systems, including an inventory of working or repairable instrument sensors and a survey of the electrical integrity of all internal cable runs.

Stability of the system for some years is a prerequisite of all the final options.

However, in this investigative phase it is important not to preempt the choices by, for instance, carrying out stabilizing work in such a way as to make dismantling much more difficult and costly. For example, stabilizing the contamination in certain areas using concrete would certainly reduce the potential for the spread of contamination but it would certainly affect the cost and difficulty of subsequent dismantling.

Ease of physical access, whether by personnel or by remotely operated equipment, will markedly affect the costs of further work. Thus, an important part of the information gathering exercise is to give a physical description of all the potential work spaces. Where radiation makes human access difficult or impossible, photo- grammetry1 and remote video examination provide a useful method of constructing a three dimensional layout of all visible components.

3.3. ASSESSMENT OF SITE CHARACTERISTICS

In the assessment of the options for managing the damaged reactor, the radionuclide inventory, the facility and its containment, and the site should be viewed as an integral part of the overall system, where unfavourable characteristics in one component can be compensated for by favourable characteristics in another component.

' Photogrammetry is a technique of remote surveying using precision multiview photography. Provided that a few fixed points are known within the field, computer applica- tion of geometrical principles will fix the positions and dimensions of all other items.

(21)

For example, where local geology does not exhibit high confinement, the damaged facility should be provided with efficient engineered barriers to prevent significant releases into the geosphere and the biosphere. Similarly, even with a high radionuclide inventory, immediate remedial actions can be delayed for limited periods of time in situations where the primary containment has not failed, while immediate actions have to be taken if this containment is breached.

Therefore, thq selection of appropriate cleanup/decommissioning options should be made with detailed understanding of all three components mentioned above. The major site related characteristics important in the decision making process are summarized below.

3.3.1. Geology

No changes in local geology are expected even after a severe accident.

However, if the prospect of creating a concrete structure around the damaged facility is foreseen, the actual geological situation should be reassessed from this point of view. For example, the behaviour of subsurface materials and their response to the stresses induced by a new construction will be of particular interest.

The stability assessment can be performed by means of standard methods for prediction of the physical behaviour of subsurface materials. The parameters necessary for use in numerical models include items such as:

— a description of on-site geological structure and subsurface stratigraphy, lithology, mineralogy and erosion characteristics;

— the physical and chemical properties of soil, such as their stress-strain relationships, static and dynamic strength properties and permeability parameters;

— seismic and tectonic stability characteristics.

The assessments of foundation stability should take into account bearing capacity, overturning and sliding. Methods of analysis, together with appropriate investigation programmes, are listed in specialized IAEA publications [20, 21].

3.3.2. Hydrology

The hydrosphere, including both the surface water and the groundwater, represents an important pathway by which radioactive materials can be dispersed from a damaged nuclear facility into the environment. Information on contamination of water bodies plays an important role in assessing the radiological impacts on the population after release of radioactive material into the environment.

(22)

On-site hydrology data, originally obtained from a pre-operational measurement programme (e.g. as part of the early site characterization) should be reassessed.

Where necessary, reassessment using updated and additional data on hydraulically connected water bodies in the region must be done. The objectives of this task are:

— to assess the capability of waters to dilute and disperse radioactive materials released into the aquatic environment; and

— to use the data in the pathway analysis of the radionuclides released.

Particular attention should be given to sources of drinking water and water used for other purposes, such as irrigation or fishing.

Where the site has an existing borehole (sampling wells) monitoring system as part of its environmental programme, this should be used to support and validate any theoretical modelling. Where necessary, new sampling wells could be drilled to monitor the follow-up of the accident and cleanup/decommissioning activities.

The assessment procedures, together with information needed, are described in IAEA publications related to nuclear power plant siting [22-24] and waste repository siting [21].

For the purposes of the long term safety, and thus of the selection of the preferred decommissioning option, it is also necessary to include an analysis of the water transport pathways of radionuclides from the damaged facility.

3.3.3. Local topography

In general, even after a severe accident no major changes in topographic features are expected. Nevertheless, topography can play a role in planning and managing decommissioning activities, such as the provision of access for heavy transportation equipment, and creating storage/disposal sites for contaminated soils in natural depressions. In this respect, the major topographic features should be iden- tified and evaluated.

3.3.4. Climatology

The climatological situation in the area is of importance for the assessment and thus for the choice of a detailed decommissioning option. Factors of importance include:

— Precipitation in the form of rain and snow which will influence erosion and surface water and groundwater flow;

— Wind (direction, speed, duration) which affects erosion and can cause spread of contamination;

— Temperature variation, especially freeze/thaw cycles which can have an impact on the design and lifetime of engineered structures.

(23)

3.3.5. Ecology

The interaction between all components in the ecological system which consti- tutes the local environment, and the way that this interaction is affected by the options chosen for the future of the damaged facility, are additional factors which have to be analysed and evaluated.

3.3.6. Local demography and socioeconomic aspects

The actual and projected population distribution surrounding the site that could be affected by the choice of rehabilitation or decommissioning option should be evaluated. Additionally, land and water use, socioeconomic aspects, including the locally available infrastructure (communication routes, electricity lines, health care facilities, etc.) need to be considered. Nutritional habits, including consumption of locally produced food, are important in the identification of foodchains and related radiological pathways.

3.3.7. Safety and environmental impact assessment

A safety and environmental impact assessment is a very helpful tool to evaluate the acceptability of a chosen option and can also be a component in the selection between different options. In many Member States there is a legal requirement that such an assessment be performed and reviewed by the authorities prior to approval of a decommissioning option.

After quantification of the parameters and definition of the methodology, the purpose of this assessment is to estimate the impacts on public and occupational safety o f t h e post-accident cleanup and decommissioning of the given facility. Radio- logical and non-radiological impacts of both routine activities and possible industrial and transportation accidents during post-accident cleanup and decommissioning are evaluated.

The assessments are normally based on model calculations for which generic or preferably site specific parameters are required. These include:

— radionuclide source term, including the physical/chemical forms

— geometry and boundary conditions of the water bodies

- r data of importance for water flow (hydraulic head, hydraulic conductivity, permeability, porosity, etc.)

— data of importance in the transport of radionuclides (solubility, distribution coefficient, etc.).

The content of the safety and environmental impact assessment may differ from country to country and also depend on the type of installation. In general, however, it will give a summary of all effects of the proposed activities on humans and the environment.

(24)

3.4. NATIONAL REGULATIONS

In general, regulations are in place that can be used to cover most aspects of the cleanup and decommissioning of a nuclear power reactor that has been involved in an accident.

It is unlikely that the time schedule for decommissioning a nuclear plant after a severe accident will depend on national legislation. The timetable, which most probably will be decided on a case by case basis, will be much more dependent on factors such as current status of the facility, site considerations, occupational and public exposure, and the availability of suitable equipment, experienced staff and waste disposal sites.

The cleanup and/or decommissioning of a reactor that has been involved in an accident are also subject to constraints imposed by statements, orders and amendments to the facility licence issued by the regulatory body subsequent to the accident.

These constraints may relate to such activities as the controlled venting of the reactor building atmosphere, the use of special equipment for accident cleanup operations, the storage and/or disposal of radioactive wastes, and the release of processed accident water by evaporation to the atmosphere or by discharge to a river, lake or ocean. Statements, orders and amendments to the facility licence are of necessity specific to the particular reactor and accident and would be issued on a case by case basis.

An important area of concern in the post-accident cleanup and decommissioning of a nuclear reactor is the management of the large volumes of radioactive wastes (gases, liquids and solids) that result from the accident and from cleanup and decommissioning operations. In particular, certain post-accident cleanup and decommissioning wastes will have to be carefully evaluated with regard to characteristics such as specific activity, radionuclide content, total activity inventory and waste form.

Ultimate disposition of these wastes will depend on the unique characteristics they possess and on the availability of suitable facilities for their handling, storage and disposal.

One regulatory issue which will have impact on the selection of a decommissioning option, and especially on the costs for disposal of the wastes, is the ability to exempt wastes and the site from some form of regulatory control. At present, there is international consensus on the basic principles for such exemptions [25] and the IAEA is in the process of establishing levels for the unconditional release of materials and also for the release of materials from nuclear facilities, including during decommissioning, for reuse and recycle [26]. However, exemption levels have not yet been incorporated into national legislations to any significant degree.

(25)

3.5. NEED FOR UTILIZATION OF THE SITE

An important consideration when selecting a decommissioning alternative is the present and future need for the site. Some alternatives may preclude future use of the site for nuclear power generation, or for any other purpose, for periods of up to one hundred years or maybe longer. Sites acceptable for nuclear power stations are often difficult to find and frequently even more difficult to get approved. A site already accepted and approved can be a valuable commodity, not only for nuclear power installations but for conventional electricity generation and other processes which can utilize the existing structures.

Selecting a decommissioning alternative (or rehabilitation) that will permit continued use of the site for nuclear power generation, even when that alternative may be more costly than other available choices, may be justified because of the long term need for the site. Thus, an economic analysis should be performed to compare the cost of decommissioning alternatives that would restore the availability of the site against the cost of developing and licensing another comparable site.

3.6. AVAILABILITY OF STORAGE/DISPOSAL LOCATIONS

Another factor to be considered in the selection of a cleanup or decommissioning strategy is whether there are locations available which could accept the radioactive waste for final disposal. In the absence of such facilities, interim storage of waste may be considered, either at a remote location or on the site. However, if no waste storage or disposal facilities are available or planned, there is an urgent need to initiate such planning. An on-site location should also be considered because of the obvious advantages of reduced waste transport.

If no off-site waste storage or disposal facilities are available, on-site storage under less stringent radiation protection and safety conditions than normally considered necessary may have to be adopted, since the alternative of not being able to do the work owing to lack of storage facilities would be worse. On-site disposal, however, should not be carried out until an assessment has demonstrated that the site meets the relevant national criteria for a repository.

3.7. AVAILABILITY OF CLEANUP AND DECOMMISSIONING TECHNOLOGY

The basic technology for cleanup and decommissioning is reasonably well known. However, during the planning stages, there may be problems caused, for example, by poor accessibility or by a specific operation considered for cleanup or

(26)

decommissioning. In such cases it may be necessary to develop special tools or means for remote operation or handling.

The development work often has to be followed by testing of the new equipment, training of personnel, etc. These efforts can be costly and time consuming and thus it may be necessary to remain at Stage 1 or Stage 2 decommissioning for a considerable period of time, if safety or other factors allow these options [16].

3.8. FINANCIAL UNCERTAINTIES IN IMMEDIATE OR DEFERRED DISMANTLING

Funding for decommissioning is normally allocated (although the practical details vary from country to country) long before the decision for a planned decommissioning is taken [27], However, in the case of premature decommissioning due to a severe accident, the expenses for cleanup and decommissioning will probably be much higher than for a planned shutdown and the funding allocated for normal decommissioning will not be adequate. Insurance mechanisms are available in some Member States to cover such extra expenses, although they are not always sufficient.

The lack of immediate funding may result in deferred dismantling. In the case of a dismantling deferred for decades, however, events might occur which could endanger the later availability of funds. This situation has the potential for serious consequences unless the long term integrity of the damaged plant is ensured.

4. STRATEGY FOR CLEANUP

Following management of the emergency phase, post-accident activities include accident cleanup and decommissioning. Accident cleanup comprises those activities leading to defuelling of the reactor, partial or total cleanup of contamination and processing of wastes generated by the accident. If the facility is to be retired from service, decommissioning activities are considered to begin following the accident cleanup [28, 29]. However, a totally clear distinction between cleanup and decommissioning activities might be difficult to define and implement.

For each kind of activity and each option under discussion, data have to be collected to arrive at an appropriate decision and to explain methods and conclusions (especially in relation to dose estimates) to the supervising regulatory body. With a sound methodology and appropriate documentation and presentation of facts, public confidence can be assured.

(27)

4.1. GENERAL ASPECTS

Accident cleanup activities are necessary and would be approximately the same whether the reactor is ultimately refurbished or decommissioned, and, if decommissioned, would be independent of whichever decommissioning alternative is chosen.

The rationale for this is discussed in detail in Section E. 1 of Ref. [29]. Briefly stated, decontamination during the accident cleanup period (whether for eventual restart or decommissioning) cannot be too chemically corrosive or destructive, since this could compromise the integrity of systems that must remain intact during cleanup and decommissioning, especially if a delayed decommissioning alternative is chosen. In addition, major items of equipment such as the reactor vessel, reactor coolant pumps and steam generators may not be dismantled until after accident cleanup is completed since they form part of the primary system. However, the methods used to complete certain cleanup tasks may vary, depending on whether the decision is to restart or to decommission, and, in the latter case, on the decommissioning alternative chosen.

The work required to complete specific cleanup tasks is, of course, determined by the severity of the accident.

Should there be a significant alpha contamination as a consequence of the accident, substantial problems will arise in addition to those normally associated with reactor decommissioning. Similar problems will, however, be encountered in the decommissioning of fuel reprocessing plants and experience from that field can be utilized. The main problems arise from the technical difficulties involved in monitoring the short range alpha emissions together with the low values of the acceptable levels. In bulk material such as cleanup and decommissioning waste these problems are multiplied so that there will be a substantial additional contribution to the costs of waste handling.

4.2. PREPARATION FOR POST-ACCIDENT CLEANUP ACTIVITIES In Table I, typical working steps to prepare for the post-accident cleanup are listed and an indication given against each as to whether the activity will simply contribute to the total financial cost or will in addition add to the dose budget.

Initial entries into the contaminated and damaged areas are made for the purpose of obtaining data on the radiological and physical condition of the building.

Very important for dose evaluation are measurements of contamination levels and radiation exposure values, particularly in areas where extensive work is to be carried out. Estimates of physical damage can help to define special tasks such as, for example, maintenance and repair of systems and equipment. Information about the operational status o f t h e plant systems and services is needed for planning accident cleanup operations and for preparing documents for regulatory approval. In addition, documentation of all data and information gained during monitoring of the actual

(28)

TABLE I. PREPARATORY STEPS FOR POST-ACCIDENT CLEANUP Contributes to

dose cost Entry in contaminated area and data acquisition x X

Preparation of documentation for competent authorities x

Design and fabrication of special equipment X Installation of special equipment x X

Development of detailed work plans and procedures x Selection and training of accident cleanup personnel x Filtration of airborne activity from the containment x x

state of the plant should be supplemented with precise documentation of the as-built state of the plant. Training of accident cleanup personnel in plant mock-ups helps to reduce exposure times significantly and makes it much easier to estimate the doses from actual tasks because approximate working times are known before the particular work starts.

Significant quantities of radioactive fission products are released to the containment building atmosphere as a result of a severe accident. The fission products include noble gases, iodine, and volatile and semivolatile radionuclides such as

137Cs and 90Sr. Most of the fission product noble gases have short half-lives and decay to insignificant levels prior to the start of building decontamination. The iodine isotopes also have short half-lives. The major contributors to radiation exposures inside the containment at times greater than one year after the accident are the rela- tively long lived caesium isotopes and 90Sr, which plate out on building surfaces or are retained in the accident water. An exception is the noble gas 8 5Kr, which has a 10.7 year half-life and which can also constitute a major radiological hazard to cleanup and decommissioning workers. The 85Kr must be removed from the containment building atmosphere so that workers can begin the tasks necessary to clean the building, maintain instruments and equipment, and eventually remove the damaged fuel from the reactor core. (Removal of the 85Kr from the reactor building atmosphere at TMI-2 was estimated to reduce the radiation dose rate for workers by a factor of about 4 [29].)

The release of slightly radioactive gases and liquids, to enable further entries into contaminated areas, is a principal contributor to doses to the public. Release of gases and liquids should be carried out in a carefully controlled manner and be properly monitored. It may be necessary to provide a new filtered ventilation system to control the situation.

(29)

The preparation of documentation that may be required to obtain regulatory approvals necessary to proceed with cleanup activities may be very time consuming and, therefore, is a critical factor in determining when actual cleanup operation can begin. Delays cannot be compensated for during the ongoing work and will directly influence the total cost.

For post-accident cleanup, it is cost effective to use those techniques and procedures that are in use to decontaminate a plant following normal shutdown. It is generally advantageous because estimates of the time requirements of known techniques in new situations may be more precise than estimates of time requirements of newly developed techniques, and time and costs for training of the staff are reduced. However, owing to the unpredictable circumstances of the accident, new decontamination techniques may have to be developed and tested in the field. Suffi- cient time for R&D work should then be made available. To avoid delays due to failures of equipment, reserve tools and spare parts should be kept available.

4.3. IMPLEMENTATION OF POST-ACCIDENT CLEANUP ACTIVITIES The accident cleanup period is postulated to include the following tasks:

— initial radiation survey to determine the extent of contamination;

— processing of liquids contaminated during the accident (and by decontamination operations);

— initial decontamination of building and equipment surfaces and decontamination or removal of some equipment (typical initial decontamination steps for light water reactors are listed in Table II);

— removal of spent fuel (undamaged and damaged) from the reactor;

— conditioning, packaging and removal of wastes from the cleanup operations;

— periodical and final radiation surveys to determine the extent of residual contamination after decontamination, processing of liquids, defuelling and waste removal.

TABLE II. TYPICAL INITIAL DECONTAMINATION STEPS [29]

Use of the containment spray system for remote washing of contaminated surfaces Removal and packaging of small items of contaminated equipment that are easily disposed of Use of high pressure hose wash techniques for semiremote decontamination of building surfaces and equipment

Decontamination and refurbishing of essential support systems Hands-on decontamination of selected areas

Local shielding o f ' h o t spots'

(30)

Some of these tasks require major facilities and equipment that have to be designed and fabricated during the phase of preparation for cleanup activities. It may become necessary to adapt the equipment as experience is gained in using it. Occupa- tional doses due to decontamination work can be reduced by using an effective decontamination method and remotely operated equipment where practical.

Because of the uniqueness of the situation, planning and estimating cannot be precise. Thus consideration should be given to the effects on the overall timescales and costs of uncertainties in such parameters as the levels and extent of contamination, plant damage levels and problems with novel waste forms.

Work plans should include allowances for inefficiencies and maintain a certain degree of flexibility to changing data. This also implies flexibility in the cost schedule and the fundings since the need may arise for procurement of special tools and equipment.

If appropriate filter and waste treatment systems are adopted, no significant additional radiation exposure to the public is expected to occur. Selection of cleanup and decommissioning activities should ensure maintenance of the integrity of the various barriers between the radioactive inventory and the environment.

5. STRATEGY FOR DECOMMISSIONING

Following the completion of the accident cleanup activities, decommissioning activities may begin. As a result of the accident cleanup, the decommissioning activities are considered to be not greatly affected by the condition of the plant immediately following the accident. In addition, many of the uncertain conditions will have been removed during the accident cleanup; specifically the damaged fuel core will have been removed from the reactor, the large volumes of uncontained highly radioactive water will have been processed, the large areas of contaminated building surfaces will have been treated, and construction of necessary systems and structures will have been completed. Hence, decommissioning can be carried out in a more stable environment than the accident cleanup and the task may become similar to one of conventional decommissioning. Nevertheless, there would be certain impacts on the decommissioning from the accident and the accident cleanup activities, including increased levels and spread of contamination compared to normal decommissioning, the need to decommission systems and structures built and used during accident cleanup, and the potential need to store wastes generated by the accident (and during the accident cleanup period) on the site for an extended time period [30], In addition, physical damage to the plant may compromise some systems and equipment needed for the performance of decommissioning tasks, thus necessitating repairs or substitutions and increasing the time and cost of post-accident decommissioning.

(31)

Nuclear facility

Release facility for unrestricted use

(terminate licence)

FIG. 2. Normal decommissioning and post-accident decommissioning: post-operation activi- ties flow sheet.

(32)

Figure 2 illustrates the differences between normal decommissioning and post- accident decommissioning. The technology for decommissioning of nuclear power plants after normal shutdown has been described in detail elsewhere [16, 31, 32].

5.1. GENERAL ASPECTS

There are two basic decommissioning options for a facility that has suffered an accident resulting in severe fuel damage and for which the decision has been made not to return it to service. These two options are:

— immediate dismantling (equivalent to Stage 3 decommissioning);

— long term storage followed by dismantling (equivalent to Stage 1/Stage 2 followed by Stage 3).

The selection is greatly influenced by the individual and collective doses and the costs which will be incurred as a result of a particular option. Dose estimates will need to have been reached by methods which are acceptable to the national regulatory body. Individual dose limits to be met will be set within the legal framework and in addition dose constraints may be given by the national authority to satisfy a requirement for exposures to be as low as reasonably achievable (ALARA).

The following sections provide a comparison of some of the radiation protection and safety related advantages and disadvantages of the two decommissioning options as well as guidance on the specific safety areas which need to be addressed. A comprehensive overview of factors relevant to the selection of a decommissioning alternative, after normal shutdown, is available in Refs [16, 33, 34],

5.2. IMMEDIATE DISMANTLING

If the extent and type of damage is such that it is practically impossible to envisage how the radioactive inventory can be adequately contained to allow long term safe storage to be an option, it may be safest to embark on a dismantling programme. Other reasons, however, such as the need for utilization of the site (see Section 3.5), could favour the selection of immediate dismantling. In any case, a preparation period of many months will be needed before cleanup starts. The cleanup itself will last at least several years. Dismantling can then start.

An advantage of immediate dismantling is the retention and utilization of plant expertise on the site during the actual dismantling. This expertise could lessen the potential for accidents and would avoid the dose associated with retraining of personnel. As waste is recovered and conditioned, the overall risk associated with the facility will steadily decrease.

(33)

The principal disadvantage of immediate dismantling is the high occupational exposure that could be incurred by the workforce, although this may be reduced by the extensive use of remote handling techniques. This exposure is a problem particularly with a facility that has experienced a major accident with the contamination spread throughout the facility (although the cleanup activities should have reduced this contamination considerably). There may also be a problem with the immediate availability of suitable waste disposal facilities to handle the various categories of waste resulting from the dismantling. Interim storage may be required. Repeated handling of the waste increases the probability of an accidental release and/or transportation related accidents, as well as increasing occupational exposures.

In addition to the general points noted above, certain specific considerations associated with the dismantling process are enumerated below. Similar considerations are also relevant to dismantling after; long term storage but will be mitigated by the effects of radioactive decay.

Fuel: Normally, spent fuel is removed prior to decommissioning. However, after a severe accident and cleanup, there might be some fuel remaining in the facility. Prior to the commencement of dismantling, fuel which could not be removed because it exists as films, is fused to existing structures, or is inaccessible, must be evaluated to ensure that the dismantling process will not result in recriticality, interrupt the management of decay heat or cause additional relocation of the fuel.

Occupational doses: Immediate dismantling of a damaged facility will result in significant occupational exposure. There is the potential for both overexposures of individuals as well as a large collective dose to the workforce. Adequate radiological controls, including extensive use of remote manipulation techniques, must be employed to minimize occupational doses.

Containment and control of contamination: Dismantling will result in the movement of contamination. Most of the movement will be under controlled conditions. However, there is a significant potential for inadvertent releases owing to the destructive nature of dismantling and also to uncertainties in the location, physico- chemical nature and magnitude of the post-accident contamination. Personnel control, and control of equipment, dust and debris are required. Doses to the public must be carefully monitored.

Transportation and disposal of radioactive material: Dismantling will result in large quantities of radioactive waste. This waste must be properly packaged and shipped to the appropriate disposal sites. If final waste disposal sites are unavailable then interim storage sites must be utilized. Safety considerations in the transportation of the waste should be addressed from both a radiological as well as an industrial accident perspective.

(34)

5.3. LONG TERM STORAGE FOLLOWED BY DISMANTLING

Deferring dismantling of the facility takes advantage of natural decay. Depend- ing on the length of storage, a reduction in dose rates may be realized during actual dismantling. For most facilities, however, once the short lived fission products have decayed the occupational exposure will be reduced only by a factor of two for every 30 year period of storage. This is due to the fact that the radioisotope 137Cs makes the largest contribution to the occupational exposure during deferred dismantling of a plant that has suffered an accident. A storage period of 100 years would result in a reduction in exposure by only a factor of 10. (This can be compared to the factor of almost 106 reduction in exposure from 6 0Co, the controlling nuclide for decommissioning following normal shutdown.) Therefore, long term storage appears less attractive as an alternative for limiting occupational exposure from decommissioning following an accident than it is for limiting occupational exposure from decommissioning following normal shutdown, although other factors could make long term storage necessary [29].

Additionally, long term storage followed by dismantling may take advantage of technological developments during the period of storage that may result in additional dose savings. Technological developments in decontamination procedures and techniques, robotics and remote cutting could facilitate future dismantling of the facility. Also, a storage period would result in smaller quantities of high level and intermediate level radioactive waste being generated, since decay will result in waste moving down in category. The reduced inventory results in reduced transportation related impacts since a smaller inventory would have to be transported to the waste disposal site [9].

There are a number of safety related disadvantages to long term storage followed by dismantling. During the storage period there is gradual deterioration of the structures, systems and components designed to act as barriers between the contamination and the environment. Although this is a generic problem associated with delayed dismantling it is likely to raise special issues after an accident scenario where the status of the structure may be subject to uncertainty. The deterioration may be difficult to measure and the criteria for action to ensure continued safe storage may not be easily developed. Surveillance programmes would have to be developed and measures taken to ensure the safety of the personnel involved in these programmes.

Finally, as the storage period continues, expertise in the layout, maintenance and operation of the reactor and knowledge about the accident lessens as personnel leave the facility so that at the time of dismantling there will be no one with personal experience of the facility. This expertise will have to be reacquired at the time of dismantling, with a possible corresponding penalty in occupational exposure.

To some extent the knowledge may be preserved by ensuring that all drawings are brought up to the current state, maintenance and operational procedures are carefully recorded and the whole documentation placed in a storage and retrieval system.

(35)

This is desirable in any event because even if dismantling starts soon after the accident stabilization and cleanup phases, it will continue over sufficient time for experienced staff to have left the project before completion.

In addition to the more general points so far discussed, there are a number of safety considerations which need to be addressed for a strategy involving long term storage prior to dismantling.

Fuel: (See applicable considerations in the corresponding paragraph in Section 5.2.)

Containment and control of contamination: Prior to storage of the facility, a programme must be developed to continue to maintain and improve the containment developed during accident stabilization and cleanup through the use of appropriate barriers such that the release of contamination to the environment is within national regulatory limits. Furthermore, within the facility a programme must be in place to control the spread of contamination. This control is necessary to permit access to the facility and therefore the continuance of the surveillance and monitoring programmes. This programme to contain and control contamination at the facility should evaluate the potential effects of both natural (rain, erosion, flooding, seismic activity), man-made (operator errors) and physical (corrosion, deterioration) phenomena.

Physical protection: During the storage period an adequate physical security plan must be developed to control access to the facility. Unauthorized access could result in injury to personnel as well as compromise barriers designed to protect the environment from contamination. Physical security should also extend to controlling the spread of contamination by animals or organisms that might gain access to the facility during storage.

Monitoring and surveillance: Continued safe storage of the facility can only be assured through an adequate monitoring and surveillance programme. The long term surveillance programme essentially provides the monitoring required to demonstrate that the measures taken under the heading of containment and control of contamination are meeting their objectives. The programme is thus divided into two parts: a radiological programme which monitors the final outcome in radiological terms and a technical programme which aims to anticipate and correct deterioration of the barriers before any radiological consequences occur.

The radiological programme will:

— monitor, record and evaluate any changes and movements of radioactive material inside the facility;

— monitor and assess the releases of radioactive material into the environment;

— monitor and assess the external and internal doses that the plant personnel and population around the facility may incur.

Cleanup and Decommissioning of A Nuclear Reactor After A Severe Accident | IAEA

TECHNICAL REPORTS SERIES No. 346

CLEANUP AND DECOMMISSIONING

OF A NUCLEAR REACTOR

AFTER A SEVERE ACCIDENT

TECHNICAL REPORTS SERIES No. 346

CLEANUP AND DECOMMISSIONING OF A NUCLEAR REACTOR

AFTER A SEVERE ACCIDENT

FOREWORD

CONTENTS

1. INTRODUCTION

2. MANAGEMENT AFTER A SEVERE REACTOR ACCIDENT

3. FACTORS RELEVANT TO CLEANUP AND DECOMMISSIONING AFTER A SEVERE ACCIDENT

4. STRATEGY FOR CLEANUP

5. STRATEGY FOR DECOMMISSIONING